1. Field of the Invention
The present invention relates to a method for cleaning vapour of gaseous impurities by scrubbing the vapour in several steps at different pH values, preferably in at least one acid step and one alkaline step wherein the vapour is produced by preceding evaporation of polluted fluids, wherein polluted vapour is formed by boiling in a boiler, wherein the vapour is conducted to a compressor where it is compressed, and thereafter to a heat exchanger in which clean vapour is condensed and wherein the scrubbing of the vapour is performed between the boiler and the heat exchanger.
The invention also relates to an apparatus for accomplishing the method.
The method and the apparatus may be used for cleaning and separating polluted liquids during their evaporation. As examples of this one may mention industrial waste water, degreasing water, organic liquids such as manure, food production wastes etc.
2. The Prior Art
During evaporation of polluted liquids, there will most often be problems with forming the condensed vapour without impurities. This is due to the well-known phenomenon referred to as steam distillation. In the present application impurities refer to elements that are undesirable in the clean condensed liquid fraction, which is generally water. The impurities may, e.g., be alcohols, ammonia, acetic acid, etc.
During evaporation the vapour is conducted from the evaporation location, the boiler, via a compressor to the condensation location, a heat exchanger, in which the vapour is condensed. The vapour being conducted from the boiler to the heat exchanger will contain the same gases or vapours in gaseous form as those present in liquid form in the polluted liquid in the boiler.
The combination of impurities in the gas or the vapour will depend on the substances present in the polluted liquid being evaporated. Impurities in the gas will also depend on their being miscible, finitely miscible or non-miscible. Furthermore, the partial pressures of the various components at the evaporation temperature in question will also influence the composition of the impurities in the gas.
During the evaporation process there may also occur a change of substances in ion form so that these substances are converted into gaseous form and as such appear as pollutions of the gas. Most of the substances in these polluted gases may be reconstituted in ion form in a condensate if the conditions of pressure and temperature are attuned.
Thus, during evaporation of polluted liquids there will often be problems with forming the condensed vapour without impurities. This phenomenon is also referred to as steam distillation.
A number of different principles are known for using scrubbers to clean a polluted gas of undesirable gaseous pollutions. This is known, e.g., from the disclosures of FR 2,666,330. These methods are based on conducting the polluted gas through a liquid absorbing as much as possible of the polluted gas in liquid or ion form. It is important to use liquid with acid addition if the polluted gas has an alkaline reaction and, contrarily, with alkaline addition if the polluted gas has an acid reaction. In this process it is necessary to remove steam from the gas before scrubbing is performed.
Thus, several steps may be used if both acid and alkaline substances are present in the polluted gas. In this principle, atmospheric air is used as a carrier gas for the polluted gas.
From the disclosure of CH 213,240 A a method as mentioned by way of introduction is known. Thus, it is known to produce vapour by evaporation of polluted fluids. The vapour is formed in a boiler and thereafter it is condensed in a heat exchanger. A cleaning of the vapour is performed between the boiler and the heat exchanger. In order to clean the vapour a chemical solution is introduced into a chemical apparatus in order to react with the impurities in the vapour. It is disclosed that cleaning could be effected in two steps as it is disclosed that the vapour, after passage through said chemical apparatus, is led through a washing column.
The dissolved impurities are removed from the chemical apparatus. It is not disclosed that the chemical reaction could be an acid step and an alkaline step. However, it is disclosed that an ordinary scrubbing is effected in combination with a chemical reaction in order to bind the impurities by absorption or through a chemical bond. The process would involve several means for controlling the cleaning, the admixing of chemical solution and for removing the dissolved impurities.
It is the object of the present invention to remedy disadvantages of the prior art methods and apparatuses.